Please refer into our WebDesktop sample >> WebDesktopManager >> DesktopWithShortcuts.aspx.
It seems your images relative path is incorrect.

Regards,
Handy

Hello Rolf,

I got a forwarded email regarding this issue. However, as Niven said, we are unable to replicate the issue.
Does your current sample place WebGrid in a container or something? 
However, you can also try to set the ContextMenu popup position manually.
Please try to use the codes below.

   <script language="javascript" type="text/javascript" id="WebGrid1_OnRowContextMenu">
        var x;
        var y;
        function show_coords(event) {
            if (IS.ie) {
                x = event.clientX;
                y = event.clientY;
            }
            else if (IS.moz) {
                x = event.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
                y = event.clientY + document.body.scrollTop + document.documentElement.scrollTop;
               
            }
        }
        function WebGrid1_OnRowContextMenu(controlId, rowType, rowElement, menuObject) {
            var WebGrid1 = ISGetObject(controlId);
            menuObject.Show(x, y);
            return true;
        }
    </script>

Hope this helps.

Regards,
Handy

Hello Yiannis,

I suggest you to to completely uninstall and reinstall.
The previous installer contains the same build version assemblies and scripts with current installer.
They only have different date released. Currently, there is no option to upgrade or only replace your existing scripts and assemblies. 

Regards,
Handy

I can replicate the issue in here. I will report this to our developer teams. Tank you for guiding me.

Regards,
Handy

Hello,

Weird. Based on error at the first screenshots, it said that you were missing RunTime License key. 
RunTime License key is used for deployment. So, is it deployment or development server?
I suggest you to completely uninstall the product. Please also remove the registries and let me know if it works or not.

Regards,
Handy